* Add a link to GitHub contributors in the <<credits, Other Credits>> section (internal issue 808). * Clarify the behavior of command aliases described in the <<versions,Core Revisions>> and <<initialization-functionpointers, Command Function Pointers>> sections and the registry schema document with respect to whether they are or are not the same entry point, and what the behaviour of the ftext:vkGet*ProcAddr commands is for each alias (internal issue 1462). * Update slink:VkPipelineShaderStageCreateInfo valid usage statements for writing to code:Layer and code:viewportIndex to apply to any vertex processing stage (internal issue 1475). * Make sparse image creation optional for Y'C~B~C~R~ formats in the <<features-required-format-support, Required Format Support>> section and the <<features-formats-requiring-sampler-ycbcr-conversion, Formats requiring sampler Y'C~B~C~R~ conversion for ename:VK_IMAGE_ASPECT_COLOR_BIT image views>> table (internal issue 1476). * Modify the valid usage statement for flink:vkCmdDrawIndirectByteCountEXT::pname:vertexStride to use the pname:maxTransformFeedbackBufferDataStride limit rather than the pname:maxVertexInputBindingStride limit, which is a better match for transform feedback related operations (internal issue 1487). * Changed all members of slink:VkPhysicalDevicePCIBusInfoPropertiesEXT to have the `uint32_t` type. This is an imcompatible change to an EXT that's very recently released; although this is against usual Vulkan WG policy, we discussed and consider this an acceptable risk, but have polled the mesa-dev list in case there are use cases we missed (internal issue 1492). * Set spec vetsion to 1 for `VK_GOOGLE_hlsl_functionality1` and `VK_GOOGLE_decorate_string` in `vk.xml` (internal MR 2948). * Remove redundant valid usage statement `VkImageCreateInfo-pNext-02395` (internal MR 2950). * Add `check_spec_links.py` script, use it in Gitlab CI, and fix many minor markup issues discovered by the script (internal MR 2955). * Update `BUILD.md` to the current Ruby version (2.5.3), and make some corresponding updates to per-platform build instructions (internal MR 2956). * Fix binding numbers and other details in flink:vkUpdateDescriptorSetWithTemplate.txt example code blocks (internal MR 2960). * Remove some nautovalidity="true" in `vk.xml` for NV extensions where it's clearly wrong (internal MR 2970).

* Add a special case to the <<renderpass-compatibility, Render Pass Compatibility>> rules allowing single-subpass renderpasses to be compatible even if they have different resolve attachment references (public issue 835). * Fix the miss shader binding table record address rule in the <<shader-binding-table-indexing-rules, Miss Shaders>> section to index by code:missIndex, not code:sbtOffset (public issue 875).

* Detect nested bullet points in valid usage blocks and warn about them during VUID assignment (internal issue 1382). * Update the style guide to document the process for reserving new bits in bitmask types (internal issue 1411). * Clarify for slink:VkApplicationInfo::pname:apiVersion and in the <<fundamentals-validusage-versions, Valid Usage for Newer Core Versions>> section when it is valid for an application to use a certain version of Vulkan API functionality (for an instance and for a device/physical device); and when the validation layers must generate an error (internal issue 1412). * Add optional <<memory-model-availability-visibility, transitive availability/visibility operations to the memory model, including a new pname:vulkanMemoryModelAvailabilityVisibilityChains feature for slink:VkPhysicalDeviceVulkanMemoryModelFeaturesKHR (internal issue 1460). * Add the code:StorageBuffer storage class to those in the <<interfaces-resources-descset, Descriptor Set Interface>> (internal issue 1480). * Add missing `returnedonly` tags for a number of returned extension structures that can be passed in pname:pNext chains (internal issue 1515). * Clean up and rearrange some spec language for slink:VkRenderPassCreateInfo and slink:VkAttachmentReference.txt (internal issue 1522). * Correctly round the code:OpVectorTimesScalar and code:OpMatrixTimesScalar SPIR-V operations in the <<Precision of core SPIR-V Instructions>> table (internal merge request 2996). * Work around cases in flink:vkCmdBeginTransformFeedbackEXT, flink:vkCmdEndTransformFeedbackEXT, and slink:VkPipelineCoverageModulationStateCreateInfoNV where an array parameter is `optional` but the length is not in `vk.xml`. This is an interim fix using `noautovalidity` + handcoded VU replacing those that should be autogenerated (internal issue 2944 and KhronosGroup/Vulkan-ValidationLayers#480). * Remove redundant capability validation of the code:float16 and code:int8 SPIR-V capabilities from the <<spirvenv-capabilities, Capabilities>> section, since they are already covered in the preceding table. * Update check_spec_links script, including validation for reference page open blocks. Fix errors identified by the script.

* Remove nested conditionals in valid usage statements for slink:VkFramebufferCreateInfo and flink:vkCmdPipelineBarrier by duplicating statements along ifdef/ifndef paths for VK_KHR_depth_stencil_resolve (internal issue 1527). * Clarify allowed values of <<spirv-precision-operation, SPIR-V operations near infinity>>. For very large results of operations the allowed range of return values as defined in the spec didn't include the largest finite number. In some rounding modes (eg. RTZ) the largest finite number is the correctly rounded result, so it should be allowed. * Require descriptor types to match in slink:VkCopyDescriptorSet.

* Make clear that memory types for imported host memory must be host visible in slink:VkMemoryHostPointerPropertiesEXT.txt (public issue 897). * Make <<interfaces-resources-layout, WARNING block>> into a NOTE block, per the styleguide (public pull request 916).

Internal Issues:

* Make <<textures-output-format-conversion, computation of derivatives in non-uniform flow control>> have undefined behavior (internal issue 1367). * Make behavior, not just values, undefined for <<textures-layout-validation, reads from inconsistent YCbCr layouts>> (internal issue 1366). * Consolidate version and extension behavior documentation in the <<extended-functionality, Extended Functionality>> appendix, While a great deal of text was moved from other parts of the Specification into the appendix, this just serves to simplify and make consistent discussions of versions and extensions (internal issue 1473). * Add limits for slink:VkPhysicalDeviceRayTracingPropertiesNV in the <<features-limits-types, Required Limit Types>> and <<features-limits-required, Required Limits>> tables (internal issue 1511). * Disallow <<memory-protected-memory, indirect calls within protected command buffers>> by adding valid usage statements for the related indirect dispatch and draw commands (internal issue 1513). * Add valid usage stataements to slink:VkGraphicsPipelineCreateInfo, slink:VkSubpassDescription, slink:VkSubpassDescription2KHR, slink:VkSubpassDescriptionDepthStencilResolveKHR, and slink:VkImageViewCreateInfo preventing the creation of a renderpass with attachments in formats that are not supported for rendering (internal issue 1552). * Qualify valid usage statements for slink:VkAttachmentReference::pname:layout parameter so restrictions only apply if an attachment is ename:VK_ATTACHMENT_UNUSED (internal issue 1561). * Add valid usage statement for flink:vkCmdDrawIndirectByteCountEXT restricting pname:vertexStride to be positive (internal issue 1566). * Make the `VK_EXT_sample_locations` extension depend on `VK_KHR_get_physical_device_properties2` in `vk.xml`. * Rearrange and simplify the <<interfaces-resources-layout, block layout rules>>.

* Split the old <<features, Features>> chapter into four chapters: <<features, Features>>, <<limits, Limits>>, <<formats, Formats>>, and <<capabilities, Capabilities>>, with minor edits to the introductory paragraph of each chapter. Anchor names in these chapters were changed, with corresponding effects to xrefs to these anchors elsewhere in spec markup . The purpose is to make the chunked HTML spec output load faster on what was previously a single, gigantic chapter (internal issue 1554). * Add ename:VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_NV, to the supported pipeline stages for ename:VK_ACCESS_UNIFORM_READ, ename:VK_ACCESS_SHADER_READ, and ename:VK_ACCESS_SHADER_WRITE in the <<synchronization-access-types-supported>> table. * Correct legal name of Google, LLC in vk.xml \<tags> section and a copyright statement. * Clarify that Vulkan treats the Android code:AHARDWAREBUFFER_FORMAT_R8G8B8X8_UNORM format as RGBA, and the application is responsible for forcing the X/A component to be read as 1.0, in the <<memory-external-android-hardware-buffer-formats>> table. * Clarify the vertex order of various primitive topologies, and define the order of transform feedback vertex capture based on that. This involves a lot of refactoring and cleanup in the <<drawing-primitive-topologies, Primitive Topologies>>, <<geometry-input, Geometry Shader Input Primitives>> sections, and <<vertexpostproc-transform-feedback Transform Feedback>> sections, and numerous places in the <<tessellation>> chapter,

* Remove the incorrect line from "`Initial`" to "`Invalid`" state in the <<commandbuffer-lifecycle-diagram, Lifecycle of a command buffer>> diagram (public issue 881). * Add Fuchsia platform to <<boilerplate-wsi-header-table, Window System Extensions and Headers>> table (public pull request 933). * Change the type of slink:VkBufferDeviceAddressCreateInfoEXT::pname:deviceAddress from basetype:VkDeviceSize to basetype:VkDeviceAddress. These are both typedefs of code:uint64_t, so it is an ABI-compatible change (public issue 934).

Internal Issues:

* Remove generated header files and update the CI tests to build a copy of the headers for use by the hpp-generate / hpp-compile CI stages. Targets to generate the headers will not be removed, but keeping these generated files in the repository increased the frequency of conflicts between branches when merging to master (internal issue 745). * Reword "`undefined: behavior if *action*" to "`must: not do *action*`" in the places the old terminology was used, and add a new <<writing-undefined, Describing Undefined Behavior>> section of the style guide to explain how to write such language in the future (internal issue 1579). * Move almost all Python scripts into the toplevel `scripts/` directory. Apply extensive internal edits to clean up and simplify the scripts, and try to follow PEP8 guidelines. Generalize the scripts with the use of a Conventions object controlling many aspects of output generation, to enable their use in other Khronos projects with similar requirements. Autogenerate extension interface refpages (these are experimental and may be retired going forward).